Reduction of oxides to metal



2,805,149 REDUCTION OF OXIDES TO IVIETAL Felix A. Schaufelberger, Basel, Switzerland, assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application January 16, 1957, Serial No. 634,407

This invention relates to the hydrometallurgical production of powdered metals. More particularly, this invention relates to the production of powdered copper, nickel and cobalt by chemical reduction of the corresponding cuprous, nickelous, or cobaltous oxide or hydroxide. Still more particularly, it relates to production of powdered copper, nickel and cobalt by direct gas reduction of an aqueous slurry of cuprous, nickelous or cobaltous oxide or hydroxide.

As such, this application constitutes a continuation-inpart of my copending application, Serial No. 318,331, filed November 1, 1952, now abandoned.

Various processes are known for treatment of copper, nickel and cobalt-bearing ores and the like whereby the metallic constituents may be chemically separated and recovered. Unfortunately, many of these procedures result in recovery of the copper, nickel and/ or cobalt as an oxide or hydroxide. The latter must then be further processed to recover a relatively pure metal product.

Generally, this is accomplished by dry reduction which comprises heating and subjecting the oxide or hydroxide to the action of a reducing agent such as hydrogen, car bon monoxide or carbon itself. Many techniques employing various types of equipment have been developed for practicing this procedure. Each of these, however, suffers from one or more defects. Temperature control and sintering are problems which make it difiicult to obtain a product wholly satisfactory for many powder metallurgical applications. Particular problems appear where the oxide or hydroxide has been produced by precipitation, for instance, from a mixed electrolyte. Probably the most troublesome of these is a material handling problem. In such instance, the material must be filtered and washed to remove any soluble impurities. Resultant wet solids must then be dried and transferred to the reduction chamber. Following reduction, the reduced product may have to be washed again. These operations, because of the nature of the material, are not only difiicult and repetitive, but unduly expensive.

It is, therefore, a primary object of this invention to provide a chemical reduction process which is not hampered by the above drawbacks. Such a process, moreover, should be capable of producing powdered copper, nickel and cobalt of fine, uniform particle size. It should not involve the use of unusual or expensive chemical reagents. Additionally, it should require only apparatus that is simple and relatively inexpensive.

Despite the complexity of previous operations, the objects of this invention have been met in a surprisingly simple but effective manner. Particularly is this true when considering that previous known hydrometallurgical pro cesses for producing powdered metal by gas reduction were necessarily practiced on metallic salt solutions. Solubility of the metal salt in the dissolving liquor, therefore, was a limiting factor in the use thereof. Accordingly, it is all the more surprising that the present invention is so etfective, inasmuch as the material being treated need not be dissolved, and in fact, may be treated in quiteconcentrated slurries.

A general outline of the process of this invention may be easily stated. Cuprous, nickelous or cobaltous oxide or hydroxide to be treated is first mixed with water to produce a concentrated slurry. Resultant slurry is then" subjected to an elevated temperature and a superatmospheric pressure in the presence of a reducing gas. Treatment is continued for suflicient time to effect complete reduction of substantially the entiremetal content. The

slurry is then cooled and filtered, and separated product dried.

in general, the source of oxide or hydroxide to be treated is immaterial to the practice of this invention.-

The process may be conducted on cuprous, nickelous or cobaltous oxide or hydroxide obtained in any manner.

However, since the invention is most advantageous when employed in conjunction with chemical separation and recovery processes, as described above, it will be further discussed with respect to products so obtained.

In such procedures the oxide or hydroxide is precipitated from solution and usually carries with it certain impurities. When treating such a product by dry reduction, much difiiculty is encountered, as described above,-

in first filtering and washing the product free of impurities. This difliculty is completely avoided in the instant invention. Since the oxide or hydroxide is reduced in the form of a slurry, any impurities which would be removed by extensive washing will be solubiliz-ed by the slurry liquor. Separation of the product may be done by decantation or filtration and any washing desired may be accomplished in a similar manner. Again, since the oxide or hydroxide is to be subsequently slurried, the drying steps necessary in dry reduction are eliminated.

Resultant cuprous, nickelous or cobaltous oxide or hydroxide is then slurried. An advantage of this invention is its economy resulting from the fact that large quantities of oxide or hydroxide may be treated at one time. The slurry, therefore, should be as concentrated as permissible. Concentration, however, is ,in turn governed by other considerations. For instance, the instant process overcomes the material handling problem of dry reduction since a slurry can be handled as a liquid. It is important, therefore, that the slurry be not so concentrated that it cannot be handled by pumps and allied equipment. Also, since a suspension is being treated, the reducing agent can readily make intimate contact with each particle with the result that a powder of fine uniform particle size is obtained. This effect, however, can be minimized by over concentration. Exact numerical limitations of concentration is difiicult to establish since concentration depends to some extent on the particular metal being treated. In general, however, it is possible to handle 50% slurries, and in some cases even higher. An optimum range is about 25 %-40%. The particular manner in which the slurry is prepared forms no part of this invention. Any suitable mechanical means may be employed.

After a slurry of the desired consistency has been prepared it is heated to an elevated temperature. The particular treating temperature employed may vary somewhat with the particular metal slurry being treated as well as the reducing agent employed. The temperature may range from as low as F. to as high as 500 F. and, in some instances, even higher. The optimum range, however, is from about 200 F. to about 450 F. At lower temperatures, reduction is too slow to be economical. Any advantage to be gained by using higher temperatures is usually olfset by the expense incurred in providing equipment capable of handling the correspondingly higher pressures.

Various reducing agents may be employed. However,

Patented Sept. '3, 1957 thosecontaining sulfur, such as H28 and S02, should be avoided sincetheir use results information oflproducts. containing sulfur. Hydrogen may be successfully employed and, generally, is readily available. Carbon monoxide is a suitable reducingagent although its use results in CO2 formation. Various hydrocarbon compounds'are'available but are generally tooinactivefor use. The preferred reducingagent, therefore, is hydrogen. 7

The reducing agent may be introduced into the reduction chamber before, during or after heating of slurry to the desired temperature. It may heintroduced in any way desired; For instance, the reducing agent may be introduced above the surface of'the slurry or itmay be introduced directly into the body of the slurry. -Reduction is -conducted with simultaneous agitation of the slurry. This insures intimate contact of thereducing agent with the slurried particles. Agitation may be conducted by any suitablemeans, the exact natureof which forms no part of the invention. g

Total pressures used during reduction usually will not exceed about 1000 p. s. i. g. Of this total pressure, at least about 100 p. s. i. g. will constitute reducing gas partial pressure. At the preferred operating temperature range of about 200 F. to 450 F. the optimum reducing gas partial pressure will be from about 300-600 p. s. i. g.

Treatment is continued until complete reduction of the substantially entire metal is obtained. Obviously, reduction time will depend upon the various other conditions. Under those most favorable, reduction will usually be complete in from about one to two hours or less. Reduced slurry is cooled, preferably by heat exchange with incoming unreduced slurry. Cooled slurry is then filtered and the product subjected to drying without necessity of washing. Drying preferably is conducted in a hydrogen atmosphere.

The invention is concerned with the production of copper, nickel and cobalt from cuprous, nickelous and cobaltous oxides and hydroxides, respectively. The following examples illustrate the invention. All parts are by weight unless otherwise noted.

Example 1 Nickelous hydroxide is slurried in water to form a slurry of about solids. The slurry is then heated in 'an autoclave to a temperature of 205 (land subjected to a 200 p. s. i. g. partial pressure of hydrogen for 45 minutes. After cooling, the solids are filtered and dried without washing. The product analyzes 99.8% nickel.

Example 2 In processing an ammoniacal copper leach solution, cuprous oxide is precipitated, solids filtered, washed and slurried in water to form a slurry of 25%. This slurry isthentreated. inxanautoclavefor 45 minutesat250, C. and 300 p. s. i. g. partial pressure of hydrogen. After cooling and filtering, the product is dried and found to analyze 99.9% copper.

Example. 3

Cobaltous oxide is slurried in water to forma slurry. This slurry is then treated in an autoclave for 120 minutes at a temperature of 220 'C. and a hydrogen partial pressure of 500 p. s. i. g. After cooling, the product is filtered and dried without washing. The dried product analyzesv 99.7% cobalt.

I claim:

1. A method of producing elemental metal as a powder of fine, uniform particle size which comprises: preparing a concentrated slurry in water of a compound selected from the group consisting of cuprous, nickelous and cobaltous oxides and hydroxides, the solids content of said slurry being not more than about 50%; treating said slurry by subjecting it to a temperature of about -500 F., a total pressure not exceeding about 1000 p. s. i. g. and a partial pressure of at least 100 p. s. i. g. of a non-sulfidizing References Cited in the file of this patent UNITED STATES PATENTS 1,275,232 Edison Aug. 13, 1918 1,426,517 Sulzberger Aug. 22, 1922 1,686,391 Muller et a1. Oct. 2, 1928 1,783,662 Marx et a1. Dec. 2, 1930 2,375,506 Turck May 8, 1945 2,726,151 Kern Dec. 6, 1955 OTHER REFERENCES Mellor, J'. W.: A Comprehensive Treatise on Inorganic Theoretical Chemistry, Longmans, Green 8: Co., London (1922), vol. 1, page 328. 

1. A METHOD OF PRODUCING ELEMENTAL METAL AS A POWDER OF FINE, UNIFORM PARTICLE SIZE WHICH COMPRISES: PREPARING A CONCENTRATED SLURRY IN WATER OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF CUPROUS, NICKELOUS AND COBALTOUS OXIDES AND HYDROXIDES, THE SOLIDS CONTENT OF SAID SLURRY BEING NOT MORE THAN ABOUT 50%; TREATING SAID SLURRY BY SUBJECTING IT TO A TEMPERATURE OF ABOUT 100*-500*F., A TOTAL PRESSURE NOT EXCEEDING ABOUT 1000 P.S.I.G. AND A PARTIAL PRESSURE OF AT LEAST 100 P.S.I.G. OF AN NON-SULIDIZING REDUCING GAS WHEREBY SAID SUSPENDED COMPOUND IS REDUCED TO ELEMENTAL FORM, SAID SLURRY BEING AGITATED DURING SAID TREATMENT; CONTINUING TREATMENT UNTIL REDUCTION TO METAL IS SUBSTANTIALLY COMPLETE; COOLING RESULTANT SLURRY AND COLLECTING ELEMENTAL METAL PRODUCT. 